Magneto mysteries

I'm completely flummoxed by the wiring of the one magneto in my RV-7A and maybe you can offer some advice.

I have one Lightspeed electronic ignition in the RV, and one magneto. I'm not using the fancy and pricey rotary switch that is so common on airplanes; I'm using a simple toggle switch to activate the Lightspeed, and one to activate the magneto.

The Lightspeed wiring was pretty simple: run a wire to from the Lightspeed control box to a switch, wire through a pullable 5 amp circuit breaker to battery power.

The magneto is a little bit different. It doesn't use ship power, of course. It generates its own power and, thus, spark. Simple.

I've read Bob Nuckoll's discussion of the magneto; I'm not understanding its application.

Here's how I have it wired. Tell me where I went wrong. I made a so-called P-lead, which uses a single connector shielded cable. The conductor wire attaches to a post on the magneto. The shield is pigtailed to an 18g wire, which attaches to a ground stud. I used the construction practices as specified here, except that I soldered a wire to the shield, rather than crimp a connector onto the shield. I figured it would be more durable.



And so, here's how it looks on my magneto. You can click the image for a larger version:

My understanding is that when the magneto is grounded, it is, basically, off and when it is not grounded, it is on and capable of providing electrical power to the spark plugs.

I was under the impression that it is grounded when there is connectivity between the two posts/wires. The problem is from what I can tell there is always connectivity between the two posts and, subsequently, wires; at least there is when I measure it.

I ran this wire to a toggle switch on the instrument panel, figuring that providing connectivity between the two wires "grounds" the magneto, rendering it inoperative.

Here's the wires at the toggle switch:

So, under my theory, flipping the toggle switch upside down, the "down" position establishes a connection between the two wires which grounds the magneto, making it inoperative.

But because the two wires appear to be always with connectivity, because there's continuity between the two posts as I measure it, this would appear to make the switch itself irrelevant, which means I've done something wrong in my theory of how this works.

The problem is, of course, I don't know what it is.

Top 10 Aircraft Wiring Mistakes

Marc Ausman at Vertical Power has penned a new paper, "The Top 10 Aircraft Wiring Mistakes (and How to Avoid Them)." I'm almost done with my aircraft wiring and I learned a few things, too. I'm not sure that's good or bad. I also helped edit the paper.

Here it is.

Fun with electrons

As you probably know, I'm a big fan of the Vertical Power system going in my RV-7A. It's essentially a computer that runs my electrical system, giving me all sorts of flexibility and cool new features with every software upgrade.

And therein, I have to admit, lies one of the disadvantages of the VP-50. Screw up the software upgrade, and you no longer have an electrical system. This, of course, is not a long-term problem for me because I'm not going to flying for more than a year, but if I were flying and I had tried a software upgrade, as I did on Saturday, I'd be grounded right now.

After reading the VP-50 release notes for the latest upgrade (which included the lights wig-wag figure, I was a little skittish about the prospect. First, you have to download the java environment file and install it on the C drive, which is OK unless you're trying to do this with a work computer with restricted permissions. Then you have to download the software installer and put it in the C drive and then you download the software upgrade.

That's all well and good but the lack of flexibility with regard to drive locations screamed "be careful!" And so did the cable I had to make to communicate with the computer, because it had a serial connection.

Nobody's computer has a serial port anymore, so I had to buy a ridiculously expensive ($35) cable to make the connection. And because the kid at work who administers the computer system doesn't give me permissions (pssst! It's my son), I lugged the desktop PC over on Saturday.

Saturday is a really stupid time to do a software upgrade, because there's nobody at the other end of a phone to help you out if things don't go well.

And things did not go well.

First, it took me quite awhile to get the installation program to recognize which com port the cable was using, but when it finally did, it connected fine with the VP-50, which flashed its pretty red light and reported "software upgrading" .

Everything was going swimmingly until the upgrade program reported it couldn't access a flash boot, or something -- whatever that is, and there's nothing to tell you what that is. But the instructions are pretty clear: Don't turn off the power during an upgrade.

But, at 8 p.m. on a Saturday night, I couldn't keep my master switch on all weekend, so eventually off it had to go. And when starting it back up, it reported "software fail." My electrical system was gone.

Sunday was another day and this time I figured a laptop might be more successful, so I went and bought one at Best Buy ($400, I really didn't need to buy a propeller this year, I guess) and tried getting that to work, but all of the error messages are the same.

My pals at VP are trying to work through this, and thank goodness I'm doing business with a company with terrific customer service. We're trying to determine first whether the cable is talking to the VP-50 unit. But it talked for at least a little while when it said, "Erase me."

In the meantime, I'm relieving the stress by inserting the close-tolerance bolts in the left wing. That's not working, either.

Lights! Lights! Lights!

Today, N614EF got her landing and taxi lights. It's been a good day of work at ye olde hangar and -- again -- thanks to Vertical Power, it was a simple process.

First, I ran wires to the right wing, attached it to the right taxi light, configured the Vertical Power VP-50 and...



Now, this wing is going to have to come off, but I didn't put any connectors at the wing root. Instead, I just left extra wire coiled, so I've eliminated a point of failure. Why does it have to come off? Because this is the famous edge-distance-screwup wing and I've still got to set the angle of incidence on it, and I also have to run some wires for the TruTrak autopilot, which is in this wing.

The left wing, on the other hand, is ready to be attached for good (one hopes), and so RV builder and pal Brad Benson stopped by to help lift it into position. The temporary bolts went in by hand and fairly easily. I'm hoping that's a good thing.

With the wing on, I ran the wire from the VP-50, spliced it into a wire coming from the wing, configured the VP-50 for the left landing light, and....



You'll probably have to take my word for it that both lights are on in this picture. I got wet to get it; it's raining in Minnesota today.



Incidentally, I ran out of 10 amp circuits on the VP-50, so I took the flaps motor off the VP and will put it on a regular electrical buss with a fuse. I don't need a backup system for flaps; I can land and take off without them if need be.

Now as soon as I get the software updated in the VP-50, I'll configure it and -- voila! -- I'll have wig-wagging wing lights without needing any additional wiring, switches, or relays. That's the advantage of the Vertical Power system. I wonder what need things will come in the future?

One note, the new fuel line came out great and the distance from the fuse to the attachment fitting on the fuel tank was perfect -- 3 1/2" from the rubber grommet (please note that: That measurement is from the grommet, not the fuselage skin). I know a lot of people are always looking for this measurement, so there you go. No charge.



I'm a little concerned about the right wing line. It seemed a hair short, but maybe I can get an extra 1/32" or so by messing around carefully with the line inside the fuselage. We'll see.

Check other people's work

I learned a very important lesson this evening at just the right time -- don't assume the "professionals don't screw up." Here's the deal: I was installing ground and battery power cables this evening in anticipation of testing out the com radio and transponder (and intercom). When I pulled the P-9 cable out of storage, I noticed the connector had fallen off. I checked the other end, and that pulled off. Then, I tugged on the battery-to-contactor cable (P-16) that I'd already installed and they pulled off too.



Van's issued a service bulletin on its battery cables in 2006. But I purchased these last summer. They're not cheap. I will be building my own cables now because it's unlikely I can do a worse job. Still, it pushes the project back another few weeks.

A tail tale

My goal for the winter on the project was to get an electrical system designed and to get everything in the tail of the airplane put together so I can rivet up the top skin as soon as the weather warmed and human flesh can stand holding a bucking bar for longer than 10 seconds.

Since I have relatively little electrical past the baggage area, I'm on track. A few weeks ago I laid out the strobe wire runs and on Sunday I finished up wiring the cables at the power supply end.

The Van's mounting plate for the power supply is handy, but when you really look at it, it makes a wiring run a little problematic, at least compared to the folks who stick the thing under the baggage area. I'm going to have to pick up some of the sticky nylon zip-tie mounts and stick a few on the belly to guide the strobe cables properly and keep them from flopping around.

In the picture below, you can also see that I soldered wires to the drain wire, and ground them on the j-stringer that's part of the bottom skin. I could have grounded them to the mounting plate (and I probably will do that for the power ground, but I'm not convinced there's great metal-to-metal contact there. Part of it is I'm not well schooled in how much metal-to-metal contact there needs to be there.)


The other thing I'm doing is running the antenna cable to the top of the plane. I'm going to have the antenna sticking out in the breeze where I'm sure it will work should I need to activate the emergency locator transmitter from a panel switch. Once I ditch, the plane will probably flip, making the location of questionable value, of course.


As you can see, I'm running the antenna forward along the main rib, forward of the elevator bellcrank assembly (it doesn't interfere), and then up the inside of the bulkhead back toward the exit point in the skin.

I have to order a few more DG-3 Adel clamps for this.

I have some concern about the remote magnetometer for the Dynon that has to be installed behind the 707 bulkhead, I believe. There's no current running in the antenna, of course, but I don't know if the mere presence of the wire will screw things up.

The only other wire that needs to run from the tail area, is the panel-mounted switch wire for the ELT. Once I add that -- maybe next week -- and get everything secured, I'll get the skin clecoed and buttoned up. Assuming I can find some riveting help, of course.

Video: Routing strobe wires in an RV-7A

The temperature hit the 40s this past weekend, the first time it's been above freezing since December, so a trip to the hangar was in order. I'm starting to decide on various wire routes, one of which is the strobe wires from the power supply behind the baggage compartment to the wings. I didn't like the suggested route; there's too much chance they could interfere with control columns.

I'm going to start producing more amateur video of various tasks over the rest of the construction of the RV-7A. Here's the first.